#include <stdio.h>

char get_choice(void);
char get_first(void);
int  get_int(void);
void count(void);

int main(void)
{
    int choice;
    void count(void);

    while ((choice = get_choice()) != 'q')
    {
        switch (choice)
        {
        case 'a': printf("Buy low, sell hight.\n");
                  break;
        case 'b': putchar('\a');
                  break;
        case 'c': count();
                  break;       
        default : printf("Program error!\n");
                  break;
        }
    }
    printf("Bey.\n");

    return 0;
}

void count(void)
{
    int n, i;

    printf("Count how far? Enter an integer:\n");
    n = get_int();
    for(i = 1; i <= n; i++)
        printf("%d\n", i);
    while (getchar() != '\n')
        continue;
}

char get_choice(void)
{
    int ch;

    printf("Enter the letter of your choice:\n");
    printf("a. advice       b. bell\n");
    printf("c. count        q. quit\n");
    ch = get_first();
    while ((ch < 'a' || ch > 'c') && ch != 'q')
    {
        printf("Please respond with a, b, c, or q.\n");
        ch = get_first();
    }
    
    return ch;
}

char get_first(void)
{
    int ch;

    ch = getchar();
    while (getchar() != '\n')
        continue;
    
    return ch;
}

int get_int(void)
{
    int input;
    char ch;
    
    while (scanf("%d", &input) != 1)//输入不是整数
    {
        while ((ch = getchar()) != '\n')//获取值不为空
            putchar(ch);
        printf(" is not an integer.\nPlease enter an ");
        printf("integer value, such as 25, -178, or 3: ");
    }
    
    return input;
}
// input: a ;   count   ;   two ;   d   ;   q